Mini cleaning appliance for cleaning two-phase or three-phase aerosol flows generated in an electrolytic cell for producing metals

ABSTRACT

One embodiment of the present disclosure includes enclosing the upper area of the anodes using a fabric sleeve, open at its upper and lower ends, located inside unitary bells with side holes that face the holes of perforated extraction ducts located on both sides of the cell, in an anode and cathode support structure, which are connected to the normal extraction system of the production bay, thus preventing the aerosols from reaching the environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application of InternationalApplication No. PCT/CL2012/000042, filed Aug. 10, 2012, which claimspriority of CL 1978-2011, filed Aug. 12, 2011, the content of both ofwhich is incorporated herein by reference.

BACKGROUND

The production of metals by electrolytic means is currently executedmostly by depositing the metal ion on a stainless steel plate (cathode),by applying a continuous electric current between that cathode andanother metal or metal alloy plate (anode), both submerged in an aqueoussolution generally acid (electrolyte) of the metal to be deposited. Whenthe anode used is insoluble, we speak of electrowinning the metal fromthe electrolyte, while when the anode used is made of the same metal tobe obtained, we speak of electrorefining.

In both cases, once the amount of metal deposited on the cathode hasreached an adequate thickness, the cathodes are removed from thesolution and the deposit is removed from the stainless steel plate toobtain the product. The surface accumulation of a metal on another withdecorative purposes or to protect from corrosion is also executed incells with different electrolytes, in which the anode is the metal to bedeposited and the cathode is the object to be protected or decorated.There is also the case that the anode is of a metal or insolublecompound and the metal to be deposited comes from the electrolyte inwhich it is dissolved.

These same processes are also used in the treatment of liquid waste, toreduce the number of positive ions until they are below the acceptedlimits for discarding them.

The operating conditions and those of the electrolyte are adjusted witha view to optimizing the deposit on the cathode. Thus the acidity oralkalinity, concentration of metal, temperature and the stirring of thesolution are adjusted with this purpose. These characteristics of thesolution, and principally the chemical reaction produced, originate aloosening of an acid or basic aerosol, as the case may be, from the freesurface of the electrolyte. In the case of electrowinning of copper, theanodic reaction produced in the electrolytic cells generates oxygen,which forms bubbles that carry micro-drops of acid solution into theenvironment, thus forming the acid aerosol. The presence of this aerosolcauses health problems for the operators, problems in the process andcorrosion of the structures and equipment. Efforts have been made tomitigate these negative effects with different measures, but none ofthese have solved the problem satisfactorily and some of them have evenbeen the origin of another type of problem, as is described below.

The fact that the electrolyte is generally heated to temperatures ofabout 40 or more degrees Celsius increases its evaporation into theenvironment, forming an aerosol that drags micro drops and particlescontained in it. In an attempt to minimize the free surface of theelectrolyte to reduce the evaporation, beads of expanded polystyrene oranother low density material are sprinkled on the free surface of theelectrolyte where they float. These beads are the origin of otherproblems such as, for example, when they are suctioned together with theelectrolyte by the circulation pumps they affect their operation; orwhen they are positioned between the anodes and cathodes they canproduce short-circuits, affecting the normal operation of the process;also generating an irregular surface in the copper deposit in the upperarea. In replacement of the polystyrene beads or others, Chilean patentapplication 01869-2002 has proposed the use of a solution based onessence of soap bark that is incorporated into the electrolyte alteringits composition. Other compounds that have been proposed to reduce thesurface tension are non ionic surfactants such as in Chilean PatentApplication N° 00328-2006, anti-fogging compounds with sulfate orsulphonate ends as in Chilean Patent Application N° 02892-2007, additionof anti-foamers as in Chilean Patent Application N° 02684-1999,fluoro-aliphatic surfactants as in Chilean Patent Application N°00580-1995,

Another type of solution proposed is the covers with or withoutextraction of the aerosols by suction, as in Chilean Patent ApplicationN° 2518-2005 that proposes plastic covers that float on the electrolyteand on whose free face an element is adhered that traps the fog, or asin Chilean Patent Application N° 02451-2007 that suggests the use ofmultiple covers, at the rate of two for each anode, or the thermal coveras in Chilean Patent N° 44803, or the insulating hood submerged in theelectrolyte of Chilean Patent N° 36367, or like the one indicated inU.S. Pat. No. 5,609,738(A) that consists of a multi-element system ofcovers that are located under the connecting bars of the electrodes andthat suck up the aerosol between the level of the electrolyte and thatcover located under the busbars.

Another trend is the employment of air injected via one side of thecell, together with aspiration by the other side, as indicated in U.S.Pat. No. 5,855,749(A).

Another trend is to cover the surface of each anode with fiber bags,sealed to the upper part of the anode above the level of theelectrolyte, as in U.S. Pat. No. 6,120,658.

A large part of the advantages that it is hoped to obtain with theseimprovements are diminished by the increased complexity of manufacturingtogether with the greater production and operating cost with thosesystems, or because of the alteration of the electrolyte's composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side elevation of the electrolytic cell unit of thelaboratory, with one anode and two cathodes, one of which is connectedto the current, showing a diagrammatic view of the movement of thebubbles in the lead anode, which, when they reach the surface, areattracted toward the connected cathode.

FIG. 2 shows a side elevation of the electrolytic cell unit of thelaboratory, with one anode and two cathodes, one of which is connectedto the current, showing a diagrammatic view of the movement of thebubbles in the lead anode, when a bell has been placed in the upperarea, around the anode.

FIG. 3 shows a front elevation of an anode in the electrolytic cell unitof the laboratory, showing a diagrammatic view of the movement of thebubbles on the right border of the lead anode, when an angular bell hasbeen placed in the upper area, around the anode.

FIG. 4 shows a perspective view of the bell with inferior angle andlateral holes.

FIG. 5 shows a side elevation of the electrolytic cell unit of thelaboratory, with one anode and two cathodes connected, showing adiagrammatic view of the movement of the bubbles in the lead anode, whena double angular bell has been installed in the upper area of the anodeand the anode has been covered with a cloth sleeve, open at its upperand lower ends.

FIG. 6 shows a front elevation of an anode of the electrolytic cell unitof the laboratory, in which a double angular bell has been placed in theupper area, around the anode.

FIG. 7 shows a partial vertical sectional view of one end of the anodeand cathode support structure, in which suction perforation can be seen.

FIG. 8 shows a detailed perspective view of one end of the anode andcathode support structure, to which longitudinal perforated ducts havebeen incorporated on both sides of the structure.

FIG. 9 shows a perspective view of one end of the anode and cathodesupport structure, to which the aerosol collecting ducts have beenincorporated.

FIG. 10 shows an upper plan view of the electrolytic production cell,with its upper cover and the protections on its ends.

NOMENCLATURE OF REFERENCE SIGNS

The numbers indicated in the Figures have the following meaning:

-   -   1. Lead laboratory anode    -   2. Stainless steel laboratory cathode.    -   3. Electrolyte level in the Laboratory cell.    -   4. Lower level of the Electrolyte    -   5. Upper vertical wall of the exterior bell.    -   6. Straight vertical wall of the interior bell.    -   7. Cloth sleeve, anode covering.    -   8. Perforation of the vertical wall of the interior bell of the        anode.    -   9. Inclined bottom wall of the anode's exterior bell.    -   10. Bubble generated on the anode's wall.    -   11. While rising, the bubble has distanced itself from the        anode.    -   12. Space for accumulation and bursting of bubbles, above the        electrolyte level on the sloping side of the bell.    -   13. Low energy bubble escape area.    -   14. Aerosol filtration area via the layer of foam accumulated in        the interior of the straight bell that is located above the        level of the electrolyte.    -   15. Low energy bubble accumulation area.    -   16. Perforation in the vertical exterior wall of the bell.    -   17. Groove of the exterior bell for passage of the anode.    -   18. Vertical exterior transversal wall of the bell.    -   19. Vertical exterior longitudinal wall of the bell.    -   20. Sloping inferior exterior transversal wall of the bell.    -   21. Upper left horizontal crosspiece of the bell.    -   22. Upper right horizontal crosspiece of the bell.    -   23. Cathode guide rail that rests on the upper longitudinal        angle of the structure, in whose groove the cathodes of the        electrolytic cell for industrial production of metals are        inserted.    -   24. Upper longitudinal angle, of insulating material, of the        anode and cathode support structure, under which the perforated        duct for aerosol suction is located.    -   25. Perforated longitudinal duct for aerosol suction, identical        to duct 30 of FIG. 8.    -   26. Perforation of the longitudinal suction duct located in        front of each anode of the cell for electrolytic production of        metals.    -   27. Longitudinal wall of the cell for electrolytic production of        metals.    -   28. Terminal outlet end to the suction duct of the aerosol        collector.    -   29. Open end of the longitudinal perforated suction duct,        connected to the terminal outlet end to the suction duct of the        aerosol collector.    -   30. Perforated longitudinal aerosol suction duct.    -   31. Inferior guide for anode.    -   32. American coupling type connection, which connects the        terminal of the longitudinal perforated suction duct with the        outlet duct to the suction collector.    -   33. Outlet duct to the suction collector.    -   34. End of the cell's suction duct that is connected to the        production plant's suction system.    -   35. Protection of the collecting ducts of the aerosol outlet.    -   36. Cover of the electrolytic cell for producing metals.

DESCRIPTION OF THE INVENTION

This invention is situated in the field of electrolytic deposition ofmetals, which, being generally applicable, is especially applicable inthose cases that use an anode and cathode supporting structure insidethe cell. It consists of covering each anode with individual bells, openat their upper and lower ends, provided or not provided with sleevesmade of hydrophilic fabric.

This invention is based on the grounds given below:

1. Comments

A lead anode 1, such as the one illustrated in FIG. 1, generates largeamounts of bubbles in the electrowinning process as a consequence of thesemi anodic reaction of oxidation of the anions. These bubbles rise atgreat speed on the anode's surface towards the free surface of theelectrolyte in the cell. In the area close to the free surface of theelectrolyte, the bubbles act in different ways. The careful observationof the combined different behaviors of the bubbles has been the basisthat gave origin to this invention of a Mini Purification Equipment ofacid or basic aerosols, in situ. Of the various principal mechanismsthat have been considered in the design of the Mini PurificationEquipment, that help to reduce the acid concentration of aerosols, thefollowing three mechanisms are the main ones:

-   -   a) Decreased energy of the bubbles that continue their path in        the electrolyte.    -   b) Filtration of aerosols through the layer of foam formed.    -   c) Filtering of aerosols originated by explosion of bubbles        inside the bell.

a. Decreased Energy of the Bubbles that Continue their Path in theElectrolyte:

There is a reduction of the energy in the bubble as it reaches thesurface, through the reduction of its speed due to the increase in itspath, and therefore a greater time in friction with the environment. Thelonger path and therefore the bubble's greater time of residence in theelectrolyte permit reducing its energy before it reaches the surface ofthe liquid, and the bubble gets closer to the surface with an ascentspeed much lower than the bubble's start-up speed (immediately after itis originated on the anode's surface). Therefore, if a bubble arrivesvery close to the surface, it will not have sufficient energy to burstand cause the acid or basic aerosol. There is a favoring of coalescence,permitting a greater probability of fading due to the increase of itsradius and therefore a diminution of the pressure differential; as wellas a greater frictional force with the liquid, helped by the longerpath. The increase in the residence time of the bubbles in the space ofthe electrolyte that is found inside the bell permits an encounterbetween the bubbles, thus favoring coalescence. When this phenomenonoccurs, the bubbles increase in size and therefore their radius. Anincrease in the radius of the bubbles reduces the pressure differential(external and internal) of the bubble with regard to the externalenvironment and thereby favors the fading of the bubble in the liquid.On the other hand, the tractive force is increased with the increase ofthe radius, also increasing the probability of bursting in the liquid.In both cases, the coalescence permits reducing the bubble's burstingenergy when it reaches the surface.

b) Filtration of Aerosols through the Layer of Foam Formed.

The design of the interior part of the purifier where the fabric usedhas been placed permits the formation of foam, with the help of thepressure and capillarity; this foam filters the aerosols that originatein the electrolyte and use this path to escape into the environment. Byobservation of the model employed for the experiments, one can say thatapproximately 90% of the aerosols that emanate pass through the layer offoam, and a large part of the remaining 10% come from the surface of theelectrolyte via the lateral sectors (borders).

c) Filtering of Aerosols Originated by Explosion of Bubbles Inside theBell.

The wall of the sack of the inner capillary tube (with holes in thewalls) permits filtering the aerosols originating from the bubbles thatburst on the surface of the liquid present inside the bell. After theaerosols pass through the sack, they pass through a second filter: thefoam layer. Also, a large part of these bubbles are the result ofcoalescence, a phenomenon that permits a reduction of the explosionenergy of the bubble when it reaches the surface,

2. Bell with lower angle and lateral holes.

The principal aerosol mitigation mechanism is the reduction of theenergy of the bubbles that continue on their path in the electrolyte, asexplained in paragraph a) of Item 1.

In one the embodiments of the invention, the upper area of the anode 1has been covered with a bell having straight vertical walls, such asthat illustrated in FIG. 2, that has a perforation 16 in the facespointing towards the longitudinal walls of the electrolytic cell.

In a second embodiment of the invention, the upper area of the anode 1,that crosses the groove 17, has been covered with a bell with verticalwalls 5, in its upper area, which continues downwards with slopingplanes 9, towards the center, symmetric on both sides of the anode, suchas the one illustrated in FIG. 3, with perforations 16 in the facespointing towards the longitudinal walls of the electrolytic cell. Thisbell is located above the level 3 of the electrolyte, while the slopingplanes remain submerged inside the electrolyte.

In a third embodiment of the invention, the anode 1 is covered with abell having straight vertical walls 5 above the level of the electrolyte3 in its upper area, continuing downward with walls at an angle 9,closing towards the center in the lower portion submerged in theelectrolyte, with a second bell of straight vertical walls 6 inside it,with perforations 8 in their longitudinal faces, in which the interiorfaces of the interior bell are covered with hydrophilic fabric 7, inwhich the fabric extends upwards like a collar, surrounding the anode 1.(See FIG. 5.)

In a fourth embodiment of the invention, the anode is covered with abell of straight vertical walls, made of fabric, in which its lower arearemains submerged in the electrolyte.

This invention is complemented particularly well when it is used inplants that use an anode and cathode supporting structure inside themasonry cell, such as the one illustrated in FIGS. 8 and 9, whose upperlongitudinal borders are made of angle forms 24, in which, on theinterior side of the structure, a multiplicity of guide cathodes 23 arefixed and on the interior side of the angles 24 individual perforatedducts 30 are attached with as many perforations 26 as anodes 1 areemployed in the cell, perforation that point toward the interior of thecell, between each two successive guide cathodes, facing each anodicposition, which are defined by a multiplicity of guide anodes 31,attached to the floor of the anode and cathode supporting structure.

The open ends 29 of these ducts end up in the terminals 28 that areconnected by means of American couplings 32 to the outlet ducts ofaerosols to the suction collector 33 that finishes in the end of thesuction duct of the cell 34 that is connected to the suction system ofthe production plant.

Optionally, an upper cover 36 is sometimes placed over the cell, whichconfines the aerosol between the cover, the level of the electrolyte andthe side and front walls of the cell. This cover has some grids 35 atits ends that serve as protection for the ducts that connect the cellwith the production plant's suction system.

EXAMPLE OF APPLICATION

In order to experimentally test the benefits of the mini purifier, twoexperiments were carried out at laboratory level in which, using anindustrial electrolyte typical of the electrowinning of copper, thatinvolves high contents of sulfuric acid, an acid aerosol was generatedusing a lead anode. This aerosol was first collected directly and thenpassed through the mini purifier that is the motive of this invention.

The comparison of the results of both experiments shows, as we shall seein detail later, an effectiveness of more than 90% in the cleaning ofthe acid aerosol.

The experiments were carried out under the following conditions:

-   -   Current density: 360 A/m²    -   Voltage: 2.3 V    -   Electrolysis time: 4 hours    -   Concentration of sulfuric acid (H₂SO₄): 180 g/l    -   Concentration of copper (Cu): 45 g/l    -   Electrolyte temperature: 45° C.    -   Material of the anode: Lead (Pb)    -   Material of the cathode: stainless steel 316 L    -   The mini purifier was submerged 1.9 cm in the electrolyte.

In the experiment in which the mini purifier was used, an acid aerosolwas obtained with a concentration of H₂SO₄ equivalent to less than 1mg/cubic meter of air at normal conditions, that is, at 25° C., at sealevel at 45° geographical latitude (which is abbreviated as NCM, NormalCubic Meter).

In the experiment in which the mini purifier was not used, an acidaerosol was obtained with a concentration of H₂SO₄ equivalent to 7000mg/NCM.

Consequently, it was proved that the use of the mini purifier that isthe object of this invention, in its preferred embodiment, nonlimiting,used in these experiments, is very efficient in mitigating, practicallyeliminating the acid aerosol or acid fog that is customary in theobtaining of copper by electrowinning.

It is worth remembering that Supreme Decree N° 594 fixes the limit ofacid mist at 0.8 mg/NCM and grants an adjustment for altitude of 0.55mg/NCM for plants that are located in high places close to the mountainrange.

1. Mini purifying equipment to reduce the transference into theenvironment of aerosol flows of two or three phases, generated in anelectrolytic cell for metal production, comprising closing off an upperpart of anodes with bells and fabric sleeves, wherein the bells coverthe upper area of the lateral faces and the vertical borders of ananode, and fabric sleeves located over the anode inside the bells areopen at upper and lower ends, where the lower end of the bell and of thefabric sleeve are inserted in an electrolyte.
 2. Mini purifyingequipment, according to claim 1, wherein the covering of the anodes isprovided by unitary bells having straight vertical walls, open frombelow, and with an upper horizontal wall with a longitudinal groove. 3.Mini purifying equipment, according to claim 1, wherein the covering ofthe anodes is provided by unitary bells having straight vertical walls,over the electrolyte and at an angle that closes towards the center anddownward, wherein the lower portion is submerged in the electrolyte. 4.Mini purifying equipment, according to claim 1, wherein the covering ofthe anodes is provided by unitary bells having straight vertical wallsabove the level of the electrolyte, and at an angle that closes towardsthe middle, wherein the lower portion is submerged in the electrolyte,with a second bell having straight vertical walls inside it.
 5. Minipurifying equipment, according to claim 1, wherein the covering of theanodes is provided by unitary bells having straight vertical walls abovethe level of the electrolyte, and at an angle closing towards the middleand downwards in the inferior portion submerged in the electrolyte, witha second bell of straight vertical walls inside it, in which also, theinterior walls of the interior bell are surfaced with fabric.
 6. Minipurifying equipment, according to claim 1, wherein the covering of theanodes is provided by unitary bells having straight vertical walls abovethe level of the electrolyte, and at an angle that closes towards thecenter and downward, in the lower portion submerged in the electrolyte;with a second bell inside it having straight vertical walls, withperforations in its walls, in which the interior walls of the interiorbell are surfaced with fabric, in which the fabric extends like acollar, surrounding the anode upward.
 7. Mini purifying equipment,according to claim 1, wherein the covering of the anodes is provided byunitary bells having straight vertical walls above the level of theelectrolyte, with a lower portion submerged in the electrolyte and asecond bell having straight vertical walls inside it, with perforationsin its walls.